This invention relates to the beneficiation of lead or copper-lead sulphide ore or concentrate and, more particularly, to a process for the beneficiation of lead or copper-lead sulphide ore or concentrate for the substantial removal of calcium and magnesium carbonates.
In the beneficiation of ores and the subsequent metallurgical treatments of the resulting concentrates for the recovery of metal values, the presence of calcium and magnesium carbonates results in lower grades of concentrates and imposition of smelter penalties.
In the early development of froth flotation methods of concentrating ores, bubbles of hydrogen sulphide or carbon dioxide which aided selective separation of minerals from gangue were formed by acidification of ores containing sulphides or carbonates. Reference is made to this procedure, for example, in U.S. Pat. No. 1,079,107 wherein it is noted that acid required for making bubbles may be too rapidly consumed. Controlled consumption of less sulphuric acid occurred when a bisulphate was added to the process.
U.S. Pat. No. 1,799,166 provides for treatment of zinc-bearing material with acid to convert water insoluble compounds of magnesium and calcium into relatively water soluble compounds. Sulphuric acid may be used to form magnesium sulphate and calcium sulphate. Although soluble magnesium sulphate is removed readily in a solids- liquid separation, repeated washings with water are needed to separate particles of calcium sulphate, which are only slightly soluble, from solids containing the zinc-bearing material.
The treatments of metal-bearing materials with acid according to the prior art have a number of distinct disadvantages, which include the lack of control of acid consumption which had to be corrected by addition of supplemental chemicals and the additional process steps of washing to eliminate calcium sulphate. It is noted, furthermore, that in the past, lead- and lead-copper-containing materials have not been known to be treated for the removal of magnesium and calcium carbonates.